Polyacrylamide polymers are mixed with aqueous chemical solutions to increase that solution's viscosity in a reservoir. These polymer solutions are more efficient in recovering trapped oil than solutions without polymers. A problem with using polyacrylamides is that they significantly reduce the solution injection rates into the reservoir. These lower injection rates delay oil recovery and raise recovery cost.
Several methods toward improving injectivity have been proposed: (1) using higher salinity brines (see U.S. Pat. No. 3,827,499), (2) using lower molecular weight polymers (see P. J. Shuler, D. L. Kuehne, J. T. Uhl, and G. W. Walkup, Jr.: "Improving Polymer Injectivity at West Coyote Field, California," SPE Reservoir Engineering (August 1987) 2, 271-280), and (3) preshearing the polymer solution (see Shuler et al.). While these three methods are useful, still better injectivity is needed.